Scuba diving is a unique and enjoyable recreational experience. It is estimated that, every day, over 75,000 persons participate in the sport at thousands of diving resorts and operations worldwide. In addition, various commercial and military operations utilize scuba divers to perform activities as search and rescue, salvage, underwater construction and repair activities, and military reconnaissance.
Operationally, one aspect of the uniqueness of diving is that underwater communication is extremely limited and communication between divers and the surface is almost non-existent. Visual interaction between divers is more often than not impossible, particularly when distances between divers increase and when divers are at different depths. Divers within a few feet of each other, but at different depth planes, may not have any visibility of the other diver. While the diving industry has developed several techniques to facilitate underwater communication (e.g. hand signals, writing on a slate, tapping on one's tank, and some electronic communication devices), most of them require close proximity for the communicating divers and, in the case of electronic means, are prohibitively expensive for all but industrial divers and military operations.
Limited underwater visibility exacerbates communication difficulty. The best recreational ocean diving sites around the world may have 150-200 feet of underwater visibility. Most have 60 feet or less of visibility. With few exceptions, visibility at inland sites such as lakes, rivers and quarries drops below 20 feet. Considering that ocean currents in many dive areas may have a velocity of one to two knots, a diver in perfect visibility conditions can drift out of sight in less than 60 seconds.
Visibility is further reduced by underwater topography which may include coral or rock formations. Night-diving conditions obviously limit communication even further and complicates the divemaster's supervisory responsibilities.
Major scuba-diving-certifying organizations have attempted to mitigate these risks by establishing well-accepted rules: always dive with and stay close to a “buddy”; evaluate conditions carefully and seek orientation with a local dive shop before diving; plan the dive carefully, follow the plan once underwater, surface when one becomes separated from the group; etc. The fact remains, though, that the communication options available to the average recreational diver when in distress or when separated from the group are extremely limited. In contrast with many land-based activities, divers do not have the option of carrying emergency rescue beacons or other long-range communication options. At best, some recreational divers carry only a simple whistle or inflatable tube for use at the surface.
Simple and unsophisticated antenna-based location systems have been developed in the past, such as those found in U.S. Pat. No. 7,388,512, but fail to provide reliable and accurate directional and distance location information that is useful in the low-visibility environments described above.
Furthermore, underwater communication presents complicated problems due to the tendency of electromagnetic and ultrasonic waves to attenuate or otherwise deteriorate when travelling or propagating underwater. The need for location information, as well as the need to communicate text-based messages, provides another hurdle that cannot easily be solved with known underwater communication systems. Finally, the need to add security or otherwise covert communication features to these devices adds yet another level of complication for acoustic-based communication systems.